Vacuum ultraviolet laser pulsed field ionization photoelectron study of cis-2-butene.

The vacuum ultraviolet pulsed field ionization-photoelectron spectra of supersonically cooled cis-2-butene (cis-CH[sub 3]CH==CHCH[sub 3]) have been measured in the photon energy range of 73 560–75 460 cm-1. Using the ab initio theoretical rotational constants of cis-CH[sub 3]CH==CHCH[sub 3] and its cation (cis-CH[sub 3]CH==CHCH[sub 3][SUP ARRANGE="STAGGER"]+]) and a semiempirical simulation scheme, we have obtained a good fit of the origin vibrational band with partially resolved contours of rotational branches. After taking into account the Stark shift, the ionization energy of cis-CH[sub 3]CH==CHCH[sub 3] is determined to be 73 595.0±1.5 cm[sup -1]. Guided by ab initio vibrational frequency calculations, we have also assigned the vibrational bands observed for cis-CH[sub 3]CH==CHCH[sub 3][SUP ARRANGE="STAGGER"]+] in its ground state. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]